Method for mixing a fluid mass

ABSTRACT

Method and apparatus for treating a fluid mass or stock, particularly couch stock or the like in paper making. Stock material is fed to a vessel having a mixing arrangement comprising rotatably arranged processing means. At least two processing means are caused to rotate mutually adjacent in opposite directions and substantially horizontally. The stock at the upper surface of the means is conveyed towards a wall potion of the vessel, whereby spirals arranged in an inclined manner at a core of the processing means bring the stock into channels defined by the core, by the spirals, and by the wall portion of the vessel, and further towards a constriction formed by the spiral elements running in an intermeshed manner, while a part of the stock is forced in a direction away from a discharge of the vessel.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is the national stage under 35 U.S.C. 371 ofPCT/FI99/00143, filed Feb. 23, 1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for treating a fluid masswherein a mass material is fed to vessel or trough having a mixingdevice comprising rotatably arranged processing means, wherein at leasttwo of the processing means are caused to rotate in opposite directionsand essentially horizontally adjacent to one another. The presentinvention also relates to a method for treating a couch mass or thelike, wherein couch mass and dilution water are caused to fall down intoa couch pit comprising a trough and a mixing arrangement. Thus, in moregeneral terms the present invention relates to methods for treating afluid mass or stock and especially a method for treating a couch mass orthe or the like, wherein the mass or stock material is fed to a vesselor trough having a mixing device comprising rotatably arrangedprocessing means. The present invention further relates to a processorarrangement for a fluid mass or stock, said arrangement comprising avessel or trough for the reception of the respective mass or stock, aprocessing device such as a mixing arrangment arranged in the vessel andcomprising horizontally arranged rotatable cylinder body means providedwith spirals, as well as a discharge for treated or processed mass orstock. The cylinder means comprise at least two cylinders arranged forrotation counter each other. The invention further relates to a specificuse of the method and the arrangement.

2. Technical Background

In paper manufacturing trimmed strips are cut from a wet web, andadditionally wet broke material will be generated at the wire and thepress section in connection with a web break. Usually the wet brokematerial is collected, disintegrated and diluted in a pulper comprisinga container with a powerful mixing feature and thereafter it is returnedto the process.

For the disintegration to function properly the pulper must comprise asufficient amount of mass or stock which is maintained under a powerfulmixing by the disintegration means of the pulper. During regularprocessing the amount of stock brought to the pulper corresponds to aminor part of a paper machine's production. At web breaks, changes ofquality and machine stops the amount of stock may temporarily rise to anamount corresponding to the total production capacity of the machine.

In order to achieve a satisfactory mixing and disintegration effect thestock in the pulper must be kept highly diluted and a sufficiently largevolume of mass must be kept therein. This leads to a high power demandfor the disintegration and mixing.

At a web break the water consumption rises greatly and for this purposea water reserve must be arranged corresponding to the demand at atypical web break. After the disintegration the wet broke materialusually is de-watered in a separate de-watering device for bettercorrespondence with the production consistency and for retrieving thewater therefrom.

At production changes, especially at a change of color, there will exista large amount of wet broke material from the earlier paper quality,which amount cannot be used for the next quality. The wet broke materialin circulation in the system will also make the attaining of the newpaper quality slower and results in productional losses and change-overbroke masses.

In this respect it is also of importance that the pulper can be easilyand completely emptied of its contents, which is not the case fortypical pulpers.

Many paper machines have a low and narrow wire section which does notprovide space for the construction of an appropriate pulper. In thiscase vaulting and broke stocking problems will arise and the pulperitself can be difficult to maintain and service.

Corresponding problems occur in other productions where a mass ordifferent streams of components should be processed in order to achievea homogenous mass.

Usually the wet broke mass is diluted to a 2 to 3 percent consistency ina couch pit or wire pulper. Depending on the structure of the papermachine a similar pulper may also be arranged in connection with thepress section. Depending on the size of the machine the wire pulper istypically between five and fifty cubic meters and it comprises apowerful mixer which breaks up fibre bundles and pieces of paper. For aneffective function the pulper requires a good mixing which, in turn,requires a sufficient dilution. Since the pulper works under varyingconditions the dilution usually is over-dimensioned according to themost critical situation.

3. Description of Related Art

Publication No. SE-210862 describes a device for processing a materialmass in particulate or suspension form, especially for de-fibration of acellulose material, in which device at least two band spirals arearranged mutually adjacent in a shell having inlet and outlet openings,said spirals being arranged for spaced intermeshed common rotation.Their spiral surfaces are directed generally radially.

Since the device known from SE-210862 has defined inlet and outletopenings and a mainly unbroken axial path of flow it is unsuitable forprocessing a broke mass which will fall down over the whole width of apaper machine. The axial spiral surfaces give a processing of the massin a axial direction, and the mixing of the mass which takes place doesso because the band spirals will cut through the mass, which providesonly a local turbulence and permits the mass to stagnate within thedevice. A clearance between the band spirals and said shell has alsobeen provided in order to permit this kind of mixing, and separatescrews take care of the feeding of the mass through said outlet.

U.S. Pat. No. 2,797,623 discloses a worm conveyor by which broke masscan be transported out from a paper machine. The worm conveyor comprisesa screw in which the broke in a traditional manner is brought along aflute. For this transport to function the spiral surfaces of the screwmust be arranged essentially radially. Broke falling into the conveyorwill thereby be transported straight through the conveyor without anysignificant mixing.

Publication No. DE-401033 discloses a mixing and transport arrangementhaving two intermeshed band spirals. Since they are rotating againsteach other, the material transported by them will be processed in analternating manner by one or the other of the spirals and thereby amixing action will be generated. This mixing action thus comprises thespirals moving through the material to be mixed and simultaneouslytransporting it forwards. A mixing in this kind of agitator requires aneasy flowing material and there is a risk, if the screws fill up, for astanding circulation to be caused, since the material can easily flowthrough hollow portions in the spirals.

Especially in small old paper machines the agitator in the couch pit hasbeen formed as a spiral, with the idea of its pressing the brokematerial towards the outlet of the couch pit. These spirals, however,have been inefficient in that they have not ground up the broke and havenot provided a sufficient power, and thus the broke has been able tovault and block the outlet.

From the pulper the broke is usually transported via a thickener to themachine's stock chest where it is mixed with fresh stock. This can bearranged in many ways, depending on the machine's product and equipment.It is usual to combine the thickening of broke with the recovering offibers in a disk or drum filter.

At a change of quality the broke can be directed to separate collectingtanks from which it is gradually dosed into the stock. In many cases,especially in the manufacturing of colored paper, the broke generated ata change of quality can no longer be added to the process but will bedirected to the waste water treatment where the solid material isrecovered for incineration or deposition on a waste dump.

Usually the generated broke will be struck from the wire by highpressure water which simultaneously dilutes the broke. There have,however, been developed methods for mechanically dislocating broke, onemethod used including feeding it over a guiding roll having a doctorblade. Hereby the desire has been to avoid an unnecessary dilution ofthe broke. There is, however, the problem that broke of a higherconsistency tends to vault, which is accentuated by a more difficultmixing.

The object of the present invention is to provide a method and anarrangement for an efficient continuous homogenization of a mass flow,for example wet broke in a paper machine or another fluid masscomprising more or less solid components which are to be disintegratedand/or mixed into a liquid type fluid.

One object of the invention is to minimize the processed amount of mass,which minimizes the loss of time and material at a change and shutdownof the process.

An object of the invention is also to provide a method for handling forexample wet broke of high consistency, due to which the need fordiluting water and a subsequent thickening is eliminated.

A further object of the invention is to provide (a vaulting and blockingfree handling of, for example, broke, also in narrow spaces.

A further object of the invention is to provide an energy saving methodfor handling of, for example, wet broke.

One object of the invention is to provide an apparatus capable oftreating, for example, wet broke in a small volume and one which permitsa simple and complete emptying of the same.

One object of the invention is also to provide an apparatus capable oftreating, for example, broke of a high and varying consistency.

One further object of the invention is to provide an apparatus of smalldimensions which also in narrow spaces is capable of treating, forexample, broke without a risk for vaulting and blocking.

One further object of the invention is to provide an apparatus whichunder a low energy consumption treats, for example, broke.

SUMMARY OF THE INVENTION

According to the invention the set objects are obtained by arranging, ina vessel, a system comprising spiral means operating counter to eachother and in an intermeshing fashion in such a manner that the mass atthe vessel's wall will reside in channels formed by said spirals,whereby the mass at the intermesh of said spirals will be pressed into adirection which differs from the traditional directions oftransportation for the spirals.

Thus, the method according to the present invention is characterized inthat at least two of the corresponding means are brought to rotate inopposite directions and essentially horizontally adjacent to one anotherso that the mass at the upper surface of the means is conveyed outwardstowards the respective opposite side walls of said vessel, whereby themass is brought, by several spiral elements arranged in an inclinedmanner at an essentially cylindrical core of the respective processingmeans, into generally inclined channels delimited by the core, by thewalls at respective two adjacent spiral elements, and by the vessel'swall portions adjacent to the respective spiral element, and furthertowards a constriction or choke formed by the respective intermeshingspiral elements at adjacent processing means.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a processing arrangement according to the invention, whicharrangement is used as a couch pit in a paper machine, corresponding tosection 1—1 in FIG. 2,

FIG. 2 shows a corresponding processing arrangement seen from above,

FIG. 3 shows an embodiment of the processing arrangement having tenspirals arranged on each spiral cylinder, corresponding to section 3—inFIG. 1,

FIGS. 4a and 4 b show corresponding sections in some other embodimentsof the processing arrangement,

FIG. 5 shows a section of a couch pit having a central outlet,

FIGS. 6a and 6 b show a processing arrangement having two pairs ofspiral cylinders, seem from above and, respectively, in section 6 b—6 b,and

FIG. 7 schematically shows the use of the processing arrangement as acouch pit in a paper machine.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Favorably the method comprises bringing a part of said mass to bepressed against at least one outlet arranged in the vessel, bycontrolling the spiral elements' rotation and pitch around the coreand/or the vessel's inlet and/or outlet parameters, the rest of saidmass being pressed, suitably under the impact of at least one gable endof said vessel and/or the impact of the spirals acting in an intermeshedmanner, through the channels and into a direction away from the outletand/or up over the upper surface of the processing means to join themass being fed into the process.

A method according to another embodiment of the invention, especiallyarranged for treatment of couch mass, is characterized by bringing atleast two essentially vertically arranged spiral cylinders of saidmixing arrangement to rotate in an intermeshed manner counter to eachother so that mass dropping down will be transported by said spiralsoutwards against the respective outer sides of the couch pit, where themass is drawn in into channels formed by adjacent spirals, by therespective core bodies of the cylinders and by a wall of the trough sothat the mass will be conveyed towards a constriction formed by thecylinder cores and the mutual intermesh of said spirals, whereby aportion of the mass will be pressed towards an outlet, a portion of themass will circulate in channels formed at the constriction, and surplusmass will be pressed backwards through said channels.

According to a preferred embodiment of the method the amount of dilutionwater is controlled according to the width of the down-falling paper webconstituting the couch mass, suitably to obtain a consistencycorresponding to the consistency of the fresh stock in a papermanufacturing process and suitably so that the stock is returned to amass processor without a preceding thickening. Hereby the returnedamount is suitably restricted to a pre-defined proportion of the totalstock while any surplus amount suitably will be fed to a collecting tankand/or so that, at a change in the paper machine, the level in said thepit is restricted to a minimum by controlling the rotation of the spiralcylinders, by choking the outlet or in another way.

The arrangement according to the invention is especially characterizedin that the cylinder means comprises at least two cylinders arranged forrotation counter to each other, respective spiral means extendingdirectly from the surface of each respective cylinder core to thevicinity of a respective wall section of said vessel, said cylindersbeing arranged so that the spiral means at least in pairs intermesh todefine generally inclined horizontal channels having a smaller crosssection than those channels which at each respective cylinder are formedbetween adjacent spirals, the cylinder core and a wall section of thevessel.

The direction of rotation for each respective cylinder is suitably suchthat the mass at least at the outermost cylinders is pressed by thespiral means against the side walls of the vessel and downwards alongthem towards a favorably respective semi-circular portion of the vesseland suitably towards the vessel's outlet and, respectively, towards thevessel's gable walls. The dimensions of the inlet and outlet,respectively, are suitably such that the mass, due to the rotation ofthe spiral means, is at least partially pressed through the channels ina direction away from the outlet, the system of spirals suitably beingso tight that a pressure will be built up in front of the outlet.

According to a favorable embodiment of the invention each respectivespiral cylinder comprises a core suitably in the shape of a displacementbody having a considerable diameter in relation to the total diameter ofthe spiral cylinder. The diameter of the body is suitably at least 50percent, preferably about 75 to 95 percent of the total diameter. Thenumber of spirals on each cylinder is suitably more than one, preferably4 to 40, where the spirals are arranged in such a manner that theirpitch suitably is more than three diameters per turn, the angle (α)between the outer edge of a spiral and the normal plane perpendicular tothe axis of said cylinder then being more than 45° C. This angle α ispreferably more than 60°, preferably about 65° to 85°. The spiral meansare suitably arranged around each respective cylinder core alongessentially the entire horizontal extent thereof.

According to a preferred embodiment the pitch of the spirals is suchthat the pitch corresponds to the length of the cylinder on about ½ to 1turn. Thus the channels formed by the spirals will run from the inletend of the arrangement almost to the outlet end thereof, and in certaincases, the whole way. The spirals according to the invention may in thispreferred embodiment be defined as several parallel screws arranged on acommon core, and here it should be noted that these spirals, in contrastto arrangements shown in the prior art, have such a shape and pitch thatthe processed material in practice cannot keep up with the spiral pitch,and that the spirals are not, at first hand, used for transportation ofmaterial but for mixing. The spirals do not normally gear into eachother in a mutual contact, but instead an effective mixing action isachieved by pressing the material between the spirals and in the form ofa leaking between the spiral edges and the vessel's walls.

According to an alternative embodiment the shape of the spirals is suchthat the spirals comprise a triangular, or in another manner,essentially two-dimensional cross section, while the embodimentdisclosed in the appended figures comprises essentially blade-likestructures. The dimensioning and individual structure of the spirals issuitably adapted according to the material to be processed, so that thespirals at the rotation do not to any essential degree bring air withthem, while simultaneously the material to be processed has time to flowin between the spirals.

According to one embodiment of the invention the spiral cylinders arearranged in pairs and are rotatable so that the cylinders at the outersides thereof, which sides are directed towards the vessel's wall,together with said wall or, respectively, at the area between anypossibly existing adjacent other pairs of cylinders form a nip orwedge-shaped inlets for the mass, suitably so that each respective nipor wedge-shaped portion comprises a shearing/cutting edge portionco-acting with the spiral edge. According to another embodiment morethan two spiral cylinders are arranged to interact suitably in pairs.

In the figures different embodiments are shown where the number ofoutlets varies. According to one embodiment the number of outlets isgreater than one, whereby the spiral cylinders suitably are divided insections, each leading to a respective outlet. According to anotherembodiment the outlet is centrally located, the spiral cylinders thensuitably being divided in sections, each leading toward the center.According to a further embodiment each respective outlet is centrallylocated between the cylinders of the respective interacting pair ofcylinders.

According to the invention a flow or flows to be homogenized is/areprocessed so that they are conveyed to a vessel or trough, on the bottomof which spiral shaped sets formed as intermeshing spiral cylindersrotate and feed the mass towards one or several outlet opening(s) . Thespiral cylinders, consisting of a cylindrical core and spirals closelyattached thereto, are brought to rotate so that their upper sides moveaway from each other, whereby said mass will be conveyed the outer wayaround the spiral cylinders towards their under side(s) . Here theintermeshing of the spirals will form a choked portion which partiallyprevents the mass from following the rotation of the spiral cylinder,and thus the mass will be pressed, by the spiral movement of the spiral,towards an outlet located under the spiral cylinders at their end.

The direction into which the mass will be pressed by the rotating spiralis the spiral's pitch direction, the spiral pitch being the distancebetween the spiral turns in the axial direction of the spiral cylinder.The higher the pitch the more acute the spiral angle will be, whichangle is formed between the outer edges of the spirals and a normalplane imagined with respect to the axis of the spiral cylinder.

Traditional spiral conveyors usually have a pitch corresponding to onespiral diameter or less for each turn. In such a case the spiral anglewill be 17.5° C. or less, the action of the spiral being, above all,forwarding in the direction of the axis, the mixing impact beinginsignificant. According to the present invention a mixing action isachieved by pressing the mass against a constriction between thecylinders and thus the mass is forced to flow through the channelsformed by the spirals and the core or the vessel, and especially in adirection opposite to the spiral's aforesaid forwarding direction. Inorder to intensify this impact the spirals are suitably given a higherpitch so that the spiral angle α is 45° or suitably even more,corresponding to a pitch of about 3 times the spiral diameter or more.An especially good efficiency is achieved for spiral angles of 60° ormore, corresponding to a pitch of 5.5 times the spiral diameter or more.

If one wishes to have more than one outlet the spiral cylinders aredivided into sections having different pitch angles, so that mass willbe conveyed to each of said outlets. Such outlets may be arranged atboth ends of the spiral cylinders, or centrally. For centrally arrangedoutlets, the spiral sections are favorably chosen so that the pitch ofthe spiral sections meet at the outlet, which thus will be fed from twodirections.

By utilizing multiple spirals, multiple flow channels are achieved. Byletting the outer edge of the spirals extend into the near vicinity ofthe core of an adjacent spiral cylinder, the accessible volume for eachunit of angle at the meshing point of the spirals will be half of thesame in their free portion. Simultaneously, a labyrinth is achievedwhich prevents the mass from leaving the flow channels, and thus anysurplus mass not received by the outlet will be forced to flow backwardsalong the channels in a direction which, thus, will be opposite to thedirection in which the spirals at an open rotation would convey themass.

The sides and/or the bottom of said vessel or trough are suitably shapedinto a form which rather closely follows, at least for a part of thecircumference, the periphery of the spiral cylinders. The trough aroundthe spirals is favorably shaped to have semi-cylindric bottom sectionsso that the outer edge of the spirals adjacent to the outlet will passclosely near the trough in a sector corresponding to at least thedistance between two spirals. Correspondingly, the spiral ends favorablyare arranged so that they pass near the trough gable. Thus, at least onespiral at each side will press mass towards the outlet.

Since only a portion of the mass can rotate along with the spirals, thatportion of the rest of the mass which is not conveyed towards the outletopenings will be forced into an opposite direction along channels formedby the spirals. The flow of mass will be accelerated and shearing forceswill appear in the mass. These shearing forces contribute to thedisintegration for example, fiber bundles and sheets of paper or otherconglomerates of components of the mass to be processed, whichcomponents usually are more consistent in relation to the dilutionfluid. Simultaneously, this partial flow directed counter to the mainflow of the mass will contribute to an effective mixing and equalizationof the mass composition.

To that part where the channels between the spirals are not closed bythe semi-cylindrical sections of the trough, the surplus mass will beforced forwards along the channel and up in the trough, which furthermakes the mixing in the trough more efficient. By designing saidsemi-circular sections to cover a greater or lesser portion one canaffect the portion of mass being forced backwards through saidconstriction or, respectively, forwards through the open channels.

If the transition between semi-cylindrical section and the side walls ofthe trough is made sharp the spirals will, at their rotation beyond thisedge, shear off larger pieces of mass located near this edge. Thisfacilitates the treatment of a mass comprising larger continuous sheets,which for instance may be the case for a paper machine where the couchmass has passed through a press.

Since it is desirable to have only a small amount of mass undertreatment it is favorable to design the core of the spiral cylinders asa displacement body having a relatively large diameter, favorably atleast half the spiral diameter. Especially favorably the core diametermay be about ¾ of the spiral diameter or more.

The larger the spiral pitch the higher number of spirals the spiralcylinders should comprise in order to achieve the desired channeleffect. When the number of spirals is chosen it should be taken intoconsideration that the distance between the spirals should be selectedin relation to the viscosity of the mass and the rotational speed of thespiral cylinders, so that the mass initially will have the time to fillthe channels prior to reaching the semi-cylindrical portion of thetrough. Typical combinations for the couch mass in a paper machine couldbe:

Spiral diameter Core diameter Pitch at Number of spirals mm mm eachturn, mm on the cylinder 600 300 2000 6 800 600 4000 16 1000 900 6000 40

For the homogenization of other media the dimensions may considerablydiffer from the above. For instance, for producing cosmetics, muchsmaller dimensions would be considered.

In the embodiments disclosed in the figures the spirals, as such, arerelatively thin, but according to a special embodiment of the inventionthe spirals are made of displacing spirals having a tight fit, suitablyso that adjacent spirals acting in an intermeshed manner to aconsiderable extent, suitably to 50 to 98 percent, fill up the voidspace between the cylinder cores. By such an arrangement an especiallyefficient mixing can be achieved, since the spirals constitutedisplacement bodies which totally or partially fill the channels in theconstriction between the spiral cylinders. The thus achieved choke orpartial choke of the re-flow through the channels in the constrictionraises the pressure towards the outlet and bring about an especiallyforceful processing of the mass which leaks through the channels and thenarrow slits between the spirals and the trough.

This corresponds to the action of pumping with screw pumps having apositive choke, and it can be utilized for feeding the mass forwardsthrough the outlet without separate pumps.

The shredding effect at the flow through the channels can be made moreefficient by arranging, as known per se, special shredding means at thespirals and/or at the cores.

A preferred embodiment is achieved with two spiral cylinders which arepartially surrounded by a semi-cylindrical section of the trough bottomand side, the spiral cylinders rotating away from each other, viewedfrom above, so that the treated mass will be pulled outside of the pairof spiral cylinders towards the semi-cylindrical section and further intowards the nip formed where the spirals intermesh.

The spiral cylinders are made so that the gap between them is narrow.Preferably this can be achieved by utilizing multiple spirals andfurther by providing the spiral cylinders with a cylindrical core. Thusa labyrinth is achieved which prevents the mass from circulating alongwith the cylinders.

Most preferably the bottom of the trough is designed as semi-cylindersfollowing the shape of the spiral cylinders and having a tangentialtransition to the trough side, thus constituting a wedge-like inlet.Hereby is achieved a maximally efficient mass introduction and thevolume of the trough is minimized. At the same time the emptying is madeeasier since the spiral cylinder will pass over the trough bottom in itsclose vicinity. Alternatively, the transition to the trough side canfavorably be designed as a sharp edge which together with the spiralsconstitutes a shearing tool.

In order to facilitate the emptying it is preferred to provide thetrough bottom and the spiral cylinders with a slight inclination towardsthe outlet opening. A favourable inclination is of the order of 1 to 5percent. A corresponding effect can also be achieved by making thespiral cylinders and/or the spiral elements slightly conical in acorresponding manner.

The outlet opening is suitably located in one end of the trough, nearthe gable thereof. However, inlet openings may also, as mentioned, belocated at both ends, centrally in the through or in another desiredmanner. If the inlet openings are located elsewhere than from a locationat one end, the spiral cylinder is divided into sections having adifferent direction of the spiral turn, so that the mass is fed towardsthe outlets.

The arrangement can, as above has been described, be designed and usedso that there arises a pressure towards the outlet. In order to achievea pumping function the spirals are designed, in a manner known to theexpert, so that the gap between the spirals is closed or minimized.Herein also the gap between spiral cylinder and trough should be keptsmall, suitably only a few millimeters.

For controlling the consistency of the disintegrated mass underdifferent processing conditions a dosing of dilution water is suitablyused, which is proportional to the portion of total web width which isconveyed to the couch pit. Thereby the consistency of the couch mass canbe controlled to approximately correspond to the consistency of thefresh stock, fed into the process.

The mass can also be treated by more than two spiral cylinders, in whichcase it is favorable to arrange the spiral cylinders in pairs so thateach pair of spiral cylinders function as described above. Hereby it ispreferred to arrange the pairs of spiral cylinders so that they togetherform a suction nip which draws a mass in between the spiral cylinders.If for several spiral cylinders a relatively high pressure level isdesired, outlet openings should be arranged separately for each pair ofspiral cylinders.

By the invention a compact system is achieved for treating, forinstance, a broke mass of high consistency obtained in manufacturing ofpaper. Hereby it will be possible to bring the mass directly from thebroke pit back to the process, whereby any delays in the qualityadaptation can be avoided. Especially favorably this can be performedthrough a stock preparation according to patent applicationPCT/FI96/00052 by the same inventor.

In cases where the shredding and disintegration of a fibre bundle isespecially critical, the invention can be combined with a de-stripperfor treating the outgoing flow.

This is illustrated by the following example. If two spiral cylinderswith a diameter of 600 millimeters having a core diameter of 300millimeters rotate one turn a second, the circulation in the spiralcylinders would be totally 563 liters/second for each meter of machinewidth. At a web break the production of the paper machine, 10tons/hours, corresponding to a net flow of 70 liters/second at aconsistency of 4 percent, will be discharged towards the outlet in thepressure direction of the spirals. The circulation is 493 liters/secondor 7 times larger than the net flow for each meter of width. This willflow along the channels, which provides good mixing efficiency.

One embodiment of the invention will now be described in more detailwith reference to the appended drawings wherein

FIG. 1 discloses a couch pit embodiment comprising a vessel or trough 10having a discharge 12 at one gable end 16 and a spiral cylinder 20located near a suitably semi-cylindrical portion, i.e., the bottom 11 ofthe trough 10. Sheets 30 of mass from trimmings from a paper machinefall down into the couch pit where they are collected in the form of amass generally indicated by reference 32.

FIG. 2 discloses a section I—I of the couch pit according to FIG. 1 andan arrangement of two spiral cylinders 20, 20′, each of which having acore 22 and 22′, respectively, and six spirals 24, 24′ arranged so thatthe spirals of the cylinders in the area between the cores 22, 22′intermesh, preferably so that an outer edge of said spiral cylinder's 20respective spirals 24 will be close to the spiral cylinder's 20′ core22′, whereby a gap 28 is formed as disclosed in FIG. 3. The shortestdistance between the cores 22, 22′ constitutes a constriction 26 wheresaid spirals 24, 24′ and, respectively, 24″ interlace in mutualinterdigitation.

The number of spirals 24, 24′ and 24″ may be higher or lower than sixfor each spiral cylinder. Even though the invention functions with onesingle spiral on each spiral cylinder, six spirals usually is the mostfavorable, since these are needed to provide a more efficient labyrinthin the constriction 26. If the spiral cylinder, as disclosed in FIG. 4b,is designed to have a relatively larger core, the number of spiralsshould be higher, preferably up to forty or more, depending on therelationship between the diameters of the spiral and the core.

The spirals 24, 24′, 24″ and the cores 22, 22′ form, between themselves,channels 35, 35′, and together with the semicircular portion 11 of thetrough, channels 34. Reference numeral 33 indicates such channels whichat least partially comprise portions which are located outside thetrough's 10 suitably semicircular portion 11 which essentially closelyfits against said spirals 24, 24′, 24″. Gables 16, 16′ are preferablyarranged so that the gap between the gables 16, 16′ and the spiralcylinders 20, 20′ is small, whereby the channels indicated by referencenumeral 34 at their ends will be essentially closed by said gables 16,16′. Thus, the mass conveyed by the spirals towards the nip 25 will haveits only outlet through the discharge 12 or the channels 35, 35′. At theend opposite to the discharges the channels 34 will be in direct contactwith such channels 33 which are at least partially open and thus allow aflow mainly over the top of the cylinders 20, 20′ and in a directioncounter to the rotational direction of the spiral cylinder in adirection towards the discharge 12. Here it is to be observed thatreference numerals 33, 34 and 35 indicate a relative partition of thechannels in accordance with a certain property and in a positiondisclosed in the respective Figure, and that the properties of eachspecific channel with respect to openness and constriction will changeas the relative positions of the respective channel changes due to therotation of the cylinder 20.

Seen from above the spiral cylinders 20, 20′ rotate outwards, wherebyany mass 32 in the channels 22 will be drawn, due to the rotation ofeach respective spiral cylinder, towards the semi-cylindrical portion 11of the trough and into channels 34 and further to an inner nip 25 wherethe spirals 24, 24′, 24″ intermesh, and further towards the constriction26. Due to the spiral movement of the cylinders the mass 32 will beconveyed preferably towards the discharge end of the couch pit 10, atwhich end the level of the mass 32 will rise so that a return flow 36 isformed. In the channels referred to as 34, 34′ closest to the gable 16,the gable will prevent the mass 32 from flowing forwards, and thussurplus mass will flow backwards instead as channel flows 38 alongchannels referred to as 35, 35′ through the constriction 26. Afterhaving passed the constriction 26 the speed of the mass will slow downso that the mass flow will fill up the channels. Hereby the return flow36 at the surface of the mass 32 will be conveyed over the channel flow38 which among others contributes to preventing mass sheets 32 frombeing drawn directly to the discharge 12 prior to their being subjectedto a sufficient mixing and shredding at the spiral cylinders 20, 20′.

To that part where the channels 34 are not shut by said gable 16 themass 32 which does not follow the rotation of the spiral cylinders willfavorably be forced forwards along the channels 34 towards the dischargeend to the open channels 33 and will again be drawn towards theconstriction 26. If the volume of the spiral structure itself isrelatively small and frictional losses are discounted the portion ofmass flowing forwards would be ⅔ in the present case, while the portionflowing backwards would be ⅓ of the total amount of mass circulating. Ifthe spirals displace more volume, the amount of mass flowing forwardscorrespondingly increases.

During operation trimmings from the paper machine will fall as sheets 30of paper mass down into said trough 10, whereby they are conveyed by therotating spiral cylinders 20, 20′ towards a nip 37 at the transitionbetween the sides 14 of the trough 10 and its bottom 11 and onwardstowards the constriction 26 between the spiral cylinders 20, 20′. When asufficient amount of mass has been gathered in the trough 10, the spacebetween said spirals 24, 24′, 24″ at the spiral cylinders 20, 20′ willbe filled with mass 32. Due to the rotation such mass which is locatedin the channels 33, 34 of the spirals will be conveyed towards theconstriction 26 whereby the available channel volume between the spirals24, 24′, 24″ will be reduced to about one half.

FIG. 2 discloses a pair of spiral cylinders 20, 20′ seen from above andshows how spirals 24, 24′ having opposite rotational directionsintermesh. When a spiral cylinder is chosen one should take intoconsideration to leave a sufficiently large free surface between thespirals so that the broke actually falls into said channels 33 betweenthe spirals and thus can be drawn with them into the channels 34.

FIGS. 4a and 4 b discloses other embodiments of, e.g., a couch pitdesigned in accordance with the invention, the pit being designed tohave an increased height. In FIG. 4a the spiral cylinders comprise tenspirals, in FIG. 4b twenty spirals each. The higher couch pits contain abuffer capacity for broke mass and they can be operated according to thesame principles as conventional couch pits, i.e. with a level controland variable discharge pumping. Especially FIG. 4a shows how thetransition between the side 14 and the semi-cylindrical bottom 11 of thetrough 10 is designed to have a sharp edge against which said spirals 24can cut sheets of mass. The embodiment according to FIG. 4b isespecially favorable since the high volume cores 22, 22′ will displacemass, whereby the amount of mass in the treatment arrangement is keptsmall.

FIG. 5 shows, as an example, a couch pit having a central discharge. Thespirals 24 are designed to have two sections 120, 120′ having differentturning directions so that they force the mass towards a centrallylocated discharge 12′. The Figure shows the situation during a web brokewhen in addition to trimmings 30 also broke 31 will fall into the couchpit which is loaded over its whole width. In a break situation the flowthrough the couch pit will increase to a multiple of normal operation.Then it may be favorable also to increase the rotational speed of thespiral cylinders and thereby also their shredding and pumpingefficiency. For this reason they are preferably provided with a drivingdevice having a variable rotation. For controlling the operation of thearrangement it may also be preferable to provide each respectivedischarge, and in some cases also each respective inlet, with chokemeans (not shown), thus facilitating the control of the essentialoperative parameters of the arrangement.

Since the removal of mass through the discharge is less than theconveyor capacity of the spiral cylinders 20, 20′, the mass 32 will bepressed through the constriction 26 and the gaps at the spiralcylinders, which brings about a collection of mass on top of the spiralcylinders. Also on the upper side the spiral cylinders will convey mass32 generally towards the location of the discharge 12 which will bringabout a level rise there and further to a recirculation of the surfacemass, which causes broke and trimmings to be conveyed especially awayfrom said discharge prior ro their being drawn into the channels 34.Thereby they will pass through a large portion of the spiral whichenhances the probability that fibre bundles and lumps of mass will besubjected to shredding and thus disintegrated. The same effect can alsobe seen in FIG. 1, even though the falling mass here is conveyed towardsone end of the trough.

In cases where a broad couch pit is needed it is preferred to use morethan two spiral cylinders, as disclosed in FIGS. 6a and 6 b. In thiscase four cylinders have been arranged. It is favorable to arrange thespiral cylinders in pairs 45, 45′ so that the nip 27 which is formedbetween the most central cylinders and where said cylinders draw massdownwards is made so broad that it does not prevent the movement of themass in the same manner as constrictions 26 in the upwards leading nips.When several pairs 45, 45′ of cylinders are applied it is favorable toarrange separate discharges 12″ for each pair of cylinders, whereby thepairs 45, 45′ of cylinders can build up a pressure in front of therespective discharge 12′ and effectively convey the mass 32 towards it.

FIG. 7 discloses a preferred use of a processing arrangement accordingto the invention as a couch pit in connection with a paper makingprocess where the paper machine is supplied with mass from a compactstock preparation 50 according to patent application PCT/FI96/00052 bythe same inventor. Stock is pumped to the short circulation of themachine by a stock pump 51, which is controlled so that the dry flow ofstock over a sensor 52 is kept at a desired level. The stock is dilutedin a conventional manner in a mixer pump 53 and fed over a cyclonecleaner 55 and a screen 57 to the headbox 59 and a wire section 61.Backwater draining from the wire section is distributed into partialflows in accordance with Finnish Patent No. 89728 by the same inventorand fed back to the process through air separating pumps 72 according toFinnish Patent Application No. 935853 by the same inventor. Surpluswater is fed over a level box to fibre recovery 66.

Trimmings 30 and broke 31 falling down at the paper production arebrought over a wire guide roller 56 wherefrom they are dropped into thecouch pit 10 by a doctor blade 58. Dilution water for diluting couchmass is fed by a dilution water conduit 60, the amount of water beingcontrolled by a valve 62 controlled by a valve 62 controlled by a flowregulator 64 so that the amount of water is kept proportional inrelation to the amount of couch mass fed. The dilution water isfavorably filtered or clear water from fibre recovery 66. By selectingthe consistency of the diluted couch mass so that it corresponds to theconsistency of the fed fresh stock one achieves a situation in which thewater from the fibre recovery 66 in all conditions of operation issufficient for the dilution, no water reservoir being needed for thispurpose.

During normal operation the diluted couch mass is pumped by a pump 54 tostock preparation 59. At a web break the amount of couch mass willincrease and thus also the flow of dilution water, whereby at least apart of the increased amount is fed to a broke container 68. Preferablythis is done with a broke pump 55, while the pump 54 can be dimensionedfor less flow. The discharge flow from the couch pit 10 is favorablycontrolled so that the level in the couch pit is maintained, by a pump54, constant up to a pre-defined maximum variable flow, while the brokepump 55 is started immediately when the capacity of said pump 54 hasbeen exceeded so that a pre-defined maximum level has been exceeded, inwhich case the level control is taken over by the broke pump 55 untilthe maximum level has been recovered.

The invention has been described mainly as applied to paper making andtreatment of couch mass in connection thereto. The use of the inventionis, however, not restricted to this application, but it can also beextended to many other situations. Thus, the invention can be utilizedin production and returning of, e.g., chemical engineering products,concrete, etc.

Above some favorable embodiments of the invention have been discussedbut for the expert it is clear that the invention can be varied in manyother ways within the scope of the appended claims.

What is claimed is:
 1. A method for treating a fluid mass comprisingfeeding a mass material to a vessel or trough having a mixing device;said mixing device comprising rotatably arranged processing means;wherein at least two of said processing means are caused to rotate inopposite directions and substantially horizontally adjacent to oneanother; the method further comprising conveying the mass at the uppersurface of the means out towards the respective opposite portions of thevessel or the trough, wherein the opposite portions are delimited in theradial direction of the processing means; bringing the mass, using aplurality of spiral elements arranged in an inclined manner at asubstantially cylindrical core of each respective processing means, intohorizontal channels arranged in an inclined manner; which channels aredefined the core, by opposite wall portions of respectively two adjacentspiral elements, and by wall portions of the vessel which are adjacentto the spiral elements; and bringing the mass towards a constrictionformed by intermeshed spiral elements arranged, respectively, at eachtwo of said processing means rotating in opposite directions whiledisposed adjacent to each other.
 2. The method according to claim 1further including bringing a part of the mass to be forced towards atleast one discharge arranged in the vessel or trough by controlling therotation of the spiral elements, and, respectively, the pitch of thespiral elements around the core or by additionally controlling at leastone of an inlet or outlet parameter for the vessel or trough, whileforcing the rest of the mass under the impact of at least one gable wallof the vessel or trough or under the impact of spirals working counterto each other in an intermeshed manner, or under the impact of both atleast one gable wall of the said vessel and the spirals, through thechannels and in a direction away from the discharge or over the uppersurface of the processing means, or away from the discharge as well asover the upper surface of the processing means to be combined with anadded feed of mass.
 3. A method for treating a fluid mass comprisingintroducing a mass and dilution water into a couch pit comprising avessel or trough and a mixing arrangement, the method further includingbringing at least two substantially horizontally arranged spiralcylinders of the mixing arrangement to rotate in an intermeshed mannercounter to each other, thereby conveying the mass by means of spiralsarranged at the spiral cylinders, wherein the mass falls down into thecouch pit from above; drawing the mass into channels formed by adjacentspirals by cores of the cylinders and by a wall of the vessel or trough,whereby the mass is conveyed towards a constriction formed by thecylinder cores and the intermesh of the spirals, thus forcing a part ofthe mass against at least one discharge, while re-circulating a part ofthe mass in channels formed at the constrictions; and forcing surplusback through the channels.
 4. The method according to claim 3 furthercomprising controlling the amount of dilution water in accordance withthe width of a paper web falling down, which paper web comprises a couchmass, to a consistency corresponding to the consistency of fresh stockin a paper making process.
 5. The method according to claim 4 whereinthe mass is returned to a stock processor without prior thickening. 6.The method according to claim 4 further comprising restricting an amountof couch mass returned to a pre-defined proportion of the total masswhile feeding surplus mass to a collector tank so that the level in thecouch pit is restricted at a change in a paper machine to a minimum bycontrolling the rotation of the spiral cylinders or by controlling achoke arranged at the discharge.